Solar Racking + Roof Mounting Reference

Overview

Racking + mounting is the most-overlooked critical solar component. Poor mounting causes roof leaks, panel damage, structural problems. This reference covers the system.

Components of a typical mount

Standoff / mount:

• Attaches to roof rafter
• Lag bolt OR specialty fastener
• Flashing kit around it for waterproofing

Rail:

• Horizontal or vertical aluminum rail
• Connects multiple standoffs
• Holds the panels via clamps

Clamps:

• End clamps (panel edges)
• Mid clamps (between panels)

L-foot / brackets:

• Connects standoff to rail

Grounding hardware:

• Bonds panels to racking to ground
• Required by NEC

Standoff types

Lag-bolt to rafter:

• 5/16" or 3/8" stainless steel lag bolt
• Driven through roof + into rafter (minimum 2.5" into rafter)
• Flashing kit around shaft
• Most common method

Hanger bolt + standoff:

• Stud sticks up from roof
• Standoff attaches above

Direct-to-deck:

• For roofs with strong sheathing only
• Lower load capacity
• Less common

Specialty (tile roofs, metal roofs):

• Tile hooks: hooks under tile
• Metal roof clamps: clamp to seam (no roof penetration)
• Premium products required

Flashing types

Aluminum step flashing:

• Standard for asphalt shingle
• Slid under shingle course above mount
• Sealant between

Mounting plate / base flashing:

• Wide aluminum base under standoff
• More watertight than basic flashing

EPDM rubber flashing:

• For metal roofs with no shingles
• Rubber boot around standoff stem

Tile flashing:

• Specific to tile roofs
• Larger flashing area
• May require tile hook system

Roof type considerations

Asphalt shingle (most common residential)

• Standard lag-bolt + flashing system
• Need 2.5"+ into rafter
• Flashing kit non-negotiable

Tile (concrete, clay)

• Tile must be removed for mount installation
• Tile hooks: hook under tile, mount above
• Or sledgehammer break-replace tiles
• Premium pricing due to complexity

Metal (standing seam, ribbed)

• Clamp-on to seam (no roof penetration!)
• Best option: no roof leaks possible
• Premium clamps + brackets

Flat / low-slope

• Ballasted system: weights hold mount (no penetration)
• Or specialty penetration + flashing for membrane roofs
• Often tilt-mount over flat roof

Slate

• Extremely fragile
• Specialty mounts required
• Tile hook style preferred
• Less common; specialty installer

Wind + snow loading

Each roof must be evaluated for:

• Wind load: wind speed in area; panel sail effect
• Snow load: weight of snow accumulation
• Combined load: simultaneously

Engineering design verifies that the mounting can handle local conditions:

• Hurricane areas: extra fastening
• Heavy snow areas: closer mount spacing
• High elevation: thinner air, lower load
• Sites with both extremes: premium engineering

Standard load tables exist for typical residential.

Span between mounts

Standard guideline: 4 ft maximum span between mounts.

• More mounts = stronger, more $
• Fewer mounts = weaker, less $
• Snow + wind + panel size affect spacing

For typical residential 4 ft × 6 ft panel: 2 mounts at panel ends, 1 mid (if 3-panel span).

Mount placement

On rafters (required):

• Identify rafter location through deck
• Drill pilot hole + verify rafter present
• Never mount only into deck (no holding power for sustained load)

Rafter spacing:

• Standard: 16" or 24" centers
• Mount spacing must align with rafters
• Sometimes need to add blocking between rafters

Flashing installation critical points

1. Penetration angle: roof penetration must be perpendicular to roof plane
2. Sealant placement: ABOVE the flashing (water sheds onto flashing from top)
3. Flashing extends UP slope: at least 6 inches beyond the standoff
4. No exposed lag-bolt threads: caulk/seal any exposed metal
5. Replacement flashing if reroofing: existing flashing typically not reusable

Common mounting failures

Failed flashing:

• Roof leak in 1-5 years
• Often blamed on the roof, not the solar
• Major liability for installer

Pulled-out lag bolt:

• Wind load exceeded fastener
• Bolt didn't penetrate rafter
• Catastrophic (panel + system damage)

Damaged tile:

• Cracked tile from mount installation
• Customer complaint
• Tile replacement required

Settling / panel movement:

• Loose lag bolt over years
• Annual visual inspection needed

Inspection during install

For each mount:

• Lag bolt torqued to spec
• Penetration depth verified (mark 2.5" mark on lag)
• Flashing intact
• Sealant applied appropriately
• Standoff secure

Photo every mount during install for warranty documentation.

Code requirements

Structural:

• IRC Section R907 (Reroofing) covers roof modifications
• Mounting hardware must be UL-listed
• Engineering required for non-standard installations

Wind:

• ASCE 7 wind load standards
• Local building department requirements

Snow:

• ASCE 7 snow load standards
• Local snow zone

When you need an engineer

• Custom installations
• Heavy snow / wind zones
• Older home (rafters undersized)
• Mid-roof transitions
• Custom array orientation

Engineering stamp: a modest added cost, typically required by AHJ on non-standard installs.

Grounding

NEC Article 690 requires:

• All exposed metal components bonded
• Grounding electrode connected to system
• Equipment grounding conductor sized properly

In practice:

• Grounding lugs on mounts
• Grounding wire between mounts (continuous bonding)
• Equipment ground to inverter
• Inverter ground to service panel ground

Material specifications

Aluminum (most common):

• Lightweight
• Corrosion-resistant
• Less strong than steel

Stainless steel:

• Strongest
• Most corrosion-resistant
• Heaviest
• Most expensive
• For coastal + high-wind areas

Galvanized steel:

• Strong
• Less corrosion-resistant than stainless
• Can rust at cuts
• Less common in modern residential

References

• NABCEP installation curriculum
• IRC Section R907
• ASCE 7 (wind + snow loads)
• Manufacturer mounting + flashing systems
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